The condensation reactions of aromatic aldehydes, 5,5-dimethyl-1,3-cyclohexanedione and ammonium acetate efficiently promoted by several ionic liquids under solvent-free condition to afford corresponding 3, 3, 6, 6-tetramethyl-1, 8-dioxo-9-aryl-1, 2, 3, 4, 5, 6, 7, 8, 9, 10-decahydroacridines in good yields.
Poly（vinyl chloride） supported tetraethylenepentamine （PVC-TEPA） has been found to be an efficient catalyst for the Knoevenagel condensation. A wide range of aromatic aldehydes easily undergo condensations with ethyl cyanoacetate and malononitrile in the commercial 95% ethanol in refluxing using PVC-TEPA as catalyst to afford the desired products of good purity in moderate to excellent yields. A recycling study confirmed that the catalyst could be reused, the yield of the desired condensation product were not reduced. The merits of this protocol are environmentally benign, simple operation, convenient work-up and good yields. Furthermore, the catalyst can easily be recovered and reused at five times with comparable yields.
Efficient electrophilic substitution reaction of indoles with various aromatic aldehydes were carried out with a catalytic amount of sodium hydrogensulfate monohydrate （NaHSO4·H20） in ionic liquid n-butylpyridinium tetrafluoroborate （[Bpy]BF4） to afford the corresponding bi（indolyl）methanes in excellent yields. The notable advantages of this protocol in terms of low cost of catalyst and ionic liquid, mild conditions, simple operation, short reaction time, high yields and recycling of the ionic liquid.
